The objective of this research is to elucidate the relationship between the DNA interaction of intercalating drugs and their biological activity. Dimeric analogs of biologically inactive intercalating monomers sometimes show significant antitumor activity and greatly increased DNA affinity. This correlation strengthens our presumption that DNA is the target of intercalating antitumor agents. Understanding the interaction of various new and existing compounds with chromatin is necessary for the more intelligent design of new drugs. The biological effects of intercalators may be related to their apparent profound disruptive effect on chromatin structure. The shape of the binding isotherm and the nuclease digestion profile of chromatin treated with double- and triple-intercalators will be determined and these properties compared to those determined for the corresponding monomer. New compounds will be synthesized to examine how length and flexibility of linking group and structure of chromophore influence this comparison. Topological constraints imposed by chromatin structure could propagate unwinding effects of intercalators over many base pairs. We will examine whether effects of intercalators on chromatin structure can be influenced by treatment with enzymes which relax superhelical DNA. Interpretation of some of the results on chromatin requires parallel studies on naked DNA. We will determine whether the DNA binding of these drugs exhibit a preference for the major or minor groove or for a particular base or base sequence. We will use helix coil transition profiles and circular dichroism to determine the DNA binding parameters and gel electrophoresis to determine unwinding angles for each drug. We will submit new compounds to NCI for antitumor testing.